A number of cytokines are known to bind to specific receptor proteins on the surface of target cells. Among the specific receptor proteins that have been identified are tumor necrosis factor receptors and interleukin-1 receptors. Much effort is being directed toward isolation and characterization of a number of receptors in order to study their physiological roles and to explore possible therapeutic uses. The binding of a particular target molecule by a soluble receptor administered to a patient may alleviate disorders mediated by the target molecule.
Tumor necrosis factor-xcex1 (TNFxcex1, also known as cachectin) and tumor necrosis factor-xcex2 (TNFxcex2, also known as lymphotoxin) are homologous mammalian endogenous secretory proteins capable of inducing a wide variety of effects on a large number of cell types. The great similarities in the structural and functional characteristics of these two cytokines have resulted in their collective description as xe2x80x9cTNF.xe2x80x9d Complementary cDNA clones encoding TNFxcex1 (Pennica et al., Nature 312:724, 1984) and TNFxcex2 (Gray et al., Nature 312:721, 1984) have been isolated, permitting further structural and biological characterization of TNF.
TNF proteins initiate their biological effect on cells by binding to specific TNF receptor (TNF-R) proteins expressed on the plasma membrane of a TNF-responsive cell. TNFxcex1 and TNFxcex2 were first shown to bind to a common receptor on the human cervical carcinoma cell line ME-180 (Aggarwal et al., Nature 318:665, 1985). Hohmann et al. (J. Biol. Chem. 264:14927, 1989) reported that at least two different cell surface receptors for TNF exist on different cell types, although the relationship between these TNF-Rs is unclear. These receptors have an apparent molecular mass of about 75-80 kDa and about 55-60 kDa, respectively. In addition to cell surface receptors for TNF, soluble proteins from human urine capable of binding TNF have also been identified (Peetre et al., Eur. J. Haematol. 41:414, 1988; Seckinger et al., J. Exp. Med. 167:1511, 1988; Seckinger et al., J. Biol. Chem. 64:11966, 1989; UK Patent Application, Publ. No. 2 218 101 A to Seckinger et al.; Engelmann et al., J. Biol. Chem. 264:11974, 1989).
Interleukin-1xcex1 (IL-1xcex1) and interleukin-1xcex2 (IL-1xcex2) are distantly related polypeptide hormones that play a central role in the regulation of immune and inflammatory responses. These two proteins act on a variety of cell types and have multiple biological activities. The biological activities ascribed to IL-1xcex1 and IL-1xcex2 are mediated via at least two classes of plasma membrane bound receptors which bind both IL-1xcex1 and IL-1xcex2. The IL-1 receptors expressed on B cells (referred to herein as type II IL-1 receptors) are different from IL-1 receptors detected on T cells and other cell types (referred to herein as type I IL-1 receptors).
The present invention is directed to receptors comprising a first tumor necrosis factor receptor (TNF-R) polypeptide covalently linked to a second TNF-R polypeptide. Alternatively, the receptor comprises one or two TNF-R polypeptides covalently linked to one or two interleukin-1 receptor (IL-1R) polypeptides.
The receptors preferably are produced as fusion proteins via recombinant DNA technology. The present invention provides fusion proteins comprising, as one of at least two biologically active polypeptide components, a TNF-R polypeptide. One fusion protein of the present invention comprises two TNF-R polypeptides, preferably joined via a peptide linker.
In another embodiment of the invention, the fusion protein comprises TNF-R and IL-1R. The fusion protein preferably comprises two TNF-R polypeptides and either one or two IL-1R polypeptides.
The present invention also provides isolated DNA sequences encoding the fusion proteins, recombinant expression vectors comprising such DNA sequences, host cells containing the expression vectors, and processes for producing the recombinant fusion proteins by culturing the host cells. Pharmaceutical compositions comprising a purified fusion protein as described above and a suitable diluent, carrier, or excipient are also provided by the present invention. Such compositions are useful in therapy, diagnosis, and assays for conditions mediated by tumor necrosis factor or interleukin-1.